This invention relates to valves and in particular to needle valves having soft movable seating members. This invention also relates to valve stems that contact a valve seat and at the same time do not rotate relative to the valve seat. These two needs have been known in the art for some time.
A valve stem that contacts a valve seat and at the same time does not rotate eliminates the wear and scoring caused by excessive friction. A well-known solution to this problem is a floating metal ball attached to the end of the stem as illustrated in U.S. Pat. No. 3,529,805 of Callahan. Metal balls, however, do not seal seats that have been deformed due to corrosion. Also, balls open and close an orifice quickly and thus do not have the metering characteristics of a traditional needle valve that opens the orifice gradually with a long tapered tip.
In certain process systems there exists a need for valves to carry corrosive fluids such as a flow stream carrying high velocity particulates or aggressive chemicals. These systems may also be under high pressures and elevated temperatures. There is a constant requirement in such systems to maintain the fluid control valve in good operating condition. The sealing seats of metal valves wear rapidly in corrosive environments. Because the metal seats cannot be easily repaired, it often results in the loss of the valve. Although metal valves with metal-to-metal seals are not generally preferred for corrosive environments, their low cost and high pressure capacity continue to justify their use. Exotic and expensive metals may be employed in such cases. Plastic valves offer another alternative but may actually be costlier then metal and their operating limits on pressure and temperature are drastically reduced.
A solution to a metal-to-metal sealing arrangement is a metal-to-plastic sealing arrangement or what is commonly referred to in the industry as a soft seat. The soft seat can take two forms. The traditional form involves placing the soft material in the body of the valve and another form involves securing the soft material on the stem. The present invention uses the later or what is more accurately described as a soft tip stem.
An example of a soft seat inserted in the body is shown in Nimberger""s U.S. Pat. No. 4,630,629. Alignment of the soft seats in the bodies flow path must be taken into account. Two potential leak paths exist between the soft seat and body and the soft seat and stem. Also, soft seats are difficult to replace and remove. A seat removing tool as shown in U.S. Pat. No. 5,042,151 of Walter Roush illustrates the problems of removal. Soft seats integral with the body do not rotate and therefore the stem must rotate on the seat causing excessive wear of the seat.
In U.S. Pat. No. 4,119,296 of John Scapes, the attachment of a soft tip to the stem is accomplished with the use of a screw. The present invention eliminates the screw and extra retaining parts. In U.S. Pat. No. 6,007,049 Lloyd Wass molds threads on the soft tip and screws it into the metal stem. This tip must rotate with the stem and thus against the seal during contact which results in frequent repair and replacement. Nothing limits the radial expansion or the axial travel of the tip as it is being crushed against the sealing surface.
The disadvantages of the prior art are overcome by the present invention. Improved methods and apparatus are herein provided for effectively sealing a fluid passage within a valve body.
A valve is provided wherein a soft tip is attached to a metal stem defining the soft movable sealing member. The soft tip is allowed to rotate during sealing and utilizes the retaining means as a secondary seal.
The valve stem is threaded in a valve bonnet and the bonnet is threaded into the valve body. The bonnet aligns the soft tip over an annular seat in the valve body and a torque of the valve handle moves the soft tip in an axial direction towards and away from the seat.
It is a feature of the current invention that the soft tip stem can easily replace solid metal stems that act as a traditional metal-to-metal seals in a needle valve. The shape of the soft tip stem is identical to the solid metal steam counterpart. Therefore, it can effectively convert a metal-to-metal hard seat valve into a soft seat valve by swapping out the stems and utilizing the same bonnet and valve body with no changes in the body sealing seat. Depending on the application, soft tip stems may be used as replacement parts to extend the life of a hard seat valve.
It is a further feature of the present invention to satisfy the objective of providing an improved needle valve with a soft tip that can effectively seal high pressure fluids in demanding corrosive environments with the same pressure ratings as the metal-to-metal valve.
The soft tip can easily conform to a corroded body seal that would often be a pin hole leak on metal-to-metal seals without having to apply a high torque to the valve handle. Radial expansion is controlled by enveloping a portion of the soft tip with the metal.
It is another feature that the soft tip is attached to the stem in a simple and economical way. No adhesives or threads are used. A simple form tool and press is all that is required.
It is also a feature that the two components have a simple form and are easily manufactured. The shape of the soft tip can be easily molded out of a wide variety of plastic materials. This is important when considering the fluids that are used in the valve.
These and other features and benefits of the invention will be apparent from the following detailed description and those skilled in the art, wherein reference is made to the figures in the accompanying drawings.